Revert "Revert "ATTEND-2506 Clarify duplicate attendee handling.""

Author: RoAnnC1

src/api-reference/common/attendees/v4.attendees.markdown

@@ -305,7 +305,12 @@ Content-Type: application/json
 
 ## Create Attendee<a name="create-attendee"></a>
 
-Creates a new attendee.
+Creates a new attendee. 
+
+When adding a new attendee, the system checks for duplicates based on specific fields. These fields are defined by the attendee type's "Fields for Duplicate Search" criteria.
+
+If the new attendee matches all the duplicate search fields of an existing attendee with the same type, it is considered a duplicate and the system will show an error message.
+If "Search Across Attendee Types" is enabled, the system will check for duplicate attendees across all attendee types that use the same fields for duplicate search.
 
 ### Scopes